1. Field of the Invention
The present invention relates to a charge pump, and more particularly, to a charge pump and a charging/discharging method capable of reducing a leakage current.
2. Description of the Prior Art
A phase-locked loop (PLL) generally serves as a clock generator or a frequency synchronizer and is widely applied in electronics and communications devices. The conventional PLL includes a phase detector, a charge pump, a filter and a voltage control oscillator (VCO), where one input of the phase detector is connected to the output of the VCO. The other input of the phase detector is connected to a reference frequency generator. The output of the phase detector is a function of the difference between the phases of the two input signals and is inputted to the filter via the charge pump for generating a control voltage, which is supplied to the VCO.
When the PLL needs to lock an output frequency of the VCO, the charge pump is disconnected from the phase detector to make the control voltage generated from the charge pump/filter maintain a constant value. However, at the time the charge pump is disconnected from the phase detector, a leakage current of the charge pump will enter the filter and change the control voltage of the VCO, resulting in an inaccurate output frequency of the VCO. In particular, when the phase difference between two input signals of the phase detector is very small, the output frequency of the VCO will be seriously influenced.